Electric switching mechanism



June 4, 1935. D. A, HRI TMN 2,003,782

ELECTRIC SWITCHING MECHANI SM Filed March 31, 1933 15- Sheets-Sheet l AVMDVTDR www.4 GMWSWAN ATTX June 4, 1935. A c ms-n u 2,003,782

ELECTRIC SWITCHING MECHANISM Filed Mai-ch 51, 1953 '15 Sheets-Sheet 2 Fig. 2. 5

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ELECTRIC SWITCHING MECHANISM Filed March 31, 1933 15 Sheets-Sheet 5 lNVEA/TOR I DAV/D. A CHR/$T/AN June 4, 1935. D. A. CHRISTIAN 2,003,782

ELECTRIC SWITCHING MECHANISM I Filed March 31, 1933 15 Shets-Sheet 4 //vvE/v7'oR V 04 W0 A CHR/T/AN June 4, 1935. D. A. CHRISTIAN 2,003,782

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ELECTRIC SWITCHING' MECHANI SM Filed March 31, 1933 15 Sheets-$heet 7 /NVENTOR 0A W0 ,4 CHR/ST/AN Jim 4, 1935. D, -A CHmSTIAN 2,003,782

ELECTRIC SWITCHING MECHANI SM Filed March 31, 1933 15 SheetsSheet 8 /NI/EN7'OR DAV/D A CHR/ST/A/V June 1935- D. A. CHRISTIAN 2,003,782

ELECTRIC SWITCHING MECHANISM June 4, 1935. D A HRBTIAN 2,003,782

ELETRIC SWITCHING MECHANISM Filed March 31, 1933 15 Sheets-Sheet 10 Fig. 15a.

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/NVEN7"OR DAV/D A CHR/ST/AN June 4, 1935. D. A. CHRISTIAN 2,003,732

I ELECTRIC "SWITCHING MECHANISM Filed March 31, 1933 15 Sheets-Sheet 13 Fig.1.

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ELECTRIC SWITCHING MECHANISM Filed March 31, 1933 15 Sheets-Sheet 14 m b ke I EL Fig. 18. 5

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ELECTRIC SWITCHING MECHANI SM Filed March 31, 1933 15 Sheets-Sheet 15 DAV/D A CHRIS A/v A7 Tr Patented June 4, 1935 x STATES PATENT OFFICE ELECTRIC SWITCHING MECHANISM David Adam Christian, London, England, assigner to Siemens Brothers & Company Limited, London, England Application March 31, 1933,.Serial No. 663,692 In Great Britain March 31, 193.2

11 Claims. (Cl. 179-18) This invention relates to electric switches which makes them subject to the force or conhaving a number of outlets to any one of which trol referred to.

connection may be made over the switch. One conception in which the invention is em- Switches of this character find their greatest use bodied may be referred to;

' in selectively operated systems such as auto- The outlets are in the form of bare wires 5 matic telephone systems. spaced apart and supported at intervals and In general to give connection to a particular disposed in columns of horizontal wires arcutlet a switch or some part thereof has to ranged one behind the other. execute a movement, the extent of which may A plate which may be of metal is disposed 1 depend on the outlet concerned such being transversely to the rectangular bunch or multhe case in for example the two motion selector tiple of wires the several columns of wire passas used in automatic telephone systems or again ing through apertures in the plate. The plate a number of connecting parts one to each outcarries a number of contacting members of a let may be provided; and the complete entity springy nature in each aperture one contacting l5 regarded as a switch, one of these parts being member for each wire passing t r u the selected and operated to connect to an outlet. aperture.

When a number of the former type of switches Normally a contacting member would be have access to the same group of outlets which above the corresponding wire and if the plate accordingly are multiplied over the switches, it is lowered would pass by the wire.

is feasible to use common apparatus to steer a Associated with each wire however is a guide 20 switch to a required outlet say by giving a sebar provided with a projecting part. The guide lected outlet a particular electrical potential bar is movable so that the projection can be and setting the switch in motion and arresting brought into a position to guide the flexible it at the outlet by reason of a circuit change contacting member outwards when the plate brought about by the potential. The common is dropped so as to pass over the wire and 25 apparatus is called in aid by any switch and make contact with the wire. The guide bar is released after use to serve for any other would like an outlet Wire continue over a numswitch that requires it. In the case of the latber of switch positions and'need only be moved ter type of switch the common apparatus may into its effective position while a plate is being close a circuit for operating a particular condropped. 30 necting part. The metal plate is connected to the inlet wire The present invention has in view, amongst of the switch. When the switch is used in an other things, a switch construction readily usautomatic telephone system more than one conable with common control apparatus. ductor may have to be switched and accordingly One aspect of the invention is that the outthe plate becomes a supporting member which 35 let to which the switch is to make connection is provided with several sets of contacting memis marked or distinguished from the other outhers each Set being u ated fro the Others lets not by giving the outlet a particular 6150- d the p ate- One guidfi bar y means of Su trical potential but by putting it in a position ably d p d p oje s cou d control one conto exercise a, mechanical force or t a in tact member of each so that simultaneous con- 40 respect of the connecting parts of the switch. tact i made h q s e number of out- This distinguishing of the outlet is individual let W1I8$- to the outlet in the sense that it could be car- Common mechamsm a be provlded for ried out if all the switch connecting parts were tfi the plates after use Into then normal n s1 lOl'lS.

F fa z ifig ggz g i g 2 i fififigi g The above conception contemplates that the an y contacting members engage the sides of the t wires. It is feasible to arrange the contacting This di tm of an 011F163 me j members so as to project into. horizontal aper-,

be pp at a f i of swltch. Posmons tures in the plate. In this case the outlet wires 50 multaneously entails some operation ata parmay be in the form f flat pierced Strips of ticular switch, So that O y one switch is afladder like form the treads of which are norfected. mally cleared when a plate is dropped. The

This operation in its simplest form is a moveguides here force contacting members so as to 55 ment or positioning of contact carrying parts pass behind and contact with treads. The con- 5 tacting members need to be shaped or slotted so that when a plate is dropped movement of other guides is not prevented.

The control of the movement of the several guides may be exercised in any convenient manner. For the selection of a particular one a cross bar arrangement may be employed the intersection of two bars determining a particular one which is then mechanically moved.

It is also within the scope of the present invention to make the outlet move and act as its own marker.

The switch when operated e. g. when the plate has dropped may cause disconnection of electrical parts controlling the marking.

The switch may be used also in various ways. It is possible to make it connect to two outlets at the same time in which case two guide members need to be operated or again it may serve merely to cross-connect two or more such outlet there being no inlet to the switch or again more than one switch may be operated at a time.

It will be noted that a feature of the switch is that to connect to an outlet or outlets the whole of the contacting members are given a small movement but one or a specified number only are made effective consequent on mechanical operation on the multiple which mechanical operation need only be of temporary duration.

Varying means may be employed to control the operation of the switch. For instance the switch when taken into use may make a preliminary movement to close contacts to call in the control apparatus and a further movement when the multiple of outlets has been marked. The latter movement may also cause disconnection of the electrical parts controlling the marking. Electromagnetic control may play a part in the switch movement, controlling the preliminary movement and the later movement. The same magnet may by being 'de-energized when the switch is no longer required, place the switch in a position to be restored to normal.

For the clearer understanding of the invention reference will now be had to the accompanying drawings but it should be distinctly understood that these are shown by way of example only and considerable modifications of construction and circuit details are possible without departing from the spirit of the invention.

One embodiment of the invention is shown by way of example in Figs. 1 to 12 and a modification is shown in Fig. 13.

Figs. 14-. to 18 each of which has been divided into two parts A and. B show circuit diagrams suitable for controlling the mechanisms illustrated.

More particularly Fig. 1 shows a front view of a switch assembly with common controlling mechanism on the right of the switches. Ten switches are shown the ends of the switches appearing in the figure, the switches being inserted and withdrawn from the assembly in a direction at right angles to the plane of the paper. Extending partly across the assembly is a sectional view showing in partly superimposed sections from left to right a set of multiple conductors for an outlet choice, a guide rod associated with that multiple, a supporting bar for the guide rods, and multiple conductors, a guide rod and a set of multiple conductors associated with that guide rod, the guide rods and test conductor of the multiple extending into the common apparatus part. One transverse rod on which the supporting bar carrying the guide rods and multiple is carried is also shown in section and above the superimposed section is a sectional view taken through part of a switch member on the line AA in Fig. 3. Also at the bottom of the right hand switch member is a section of a part of the switch mechanism taken along the line CC.

Fig. 2 shows an end view looking at the right hand end of Fig. 1, and shows the common controlling mechanism. Parts have been cut away to show more clearly a shift rod for the seventh row of outlets from the bottom.

Fig. 3 shows a face view of a switch member as would be seen by looking at the right hand end of Fig. 1 with the common mechanism removed. All the contacting members have not been shown but only those for two rows of outlets, viz. the sixth and seventh from the bottom. Part of the member has been cut away at the fifth row to show the method of supporting the guide rods and multiple.

Fig. 4 shows a rear View of the plate carrying the switch magnet and contact operating mechanism.

Fig. 5 shows a sectional plan view of the switch assembly and controlling mechanism taken along the line BB in Fig. l. The back of the plate on which the magnets of the common mechanism are mounted has been cut away and the magnets have been omitted from this figure in order not to complicate it.

Figs. 6 to 10 show in perspective a switch contact member and a part of a set of multiple conductors and its associated guide rod for various positions of the switch, with respect to the multiple. Fig. 11 shows an end view of the lower part of the common mechanism and is similar to Fig. 2 with the tie plate and supporting rod for the mechanism removed.

Fig. 12 is a sectional plan showing the mag-.

nets of the common mechanism of their mounting plate. The section is taken immediately above the magnets with the top plate designated 85 in Figs. 2 and 11 cut away.

Fig. 13 shows a perspective view of a modification in which. there are no guide rods running transversely to the switch assembly but in which the multiple itself is partially rotated to effect connection with a switch member. Only parts essential to the understanding of the modification are shown and part of the multiple for one outlet only and the corresponding contact member of a switch only are shown. The supporting and operating means are shown only as regards the row of outlets in which the multiple is one it being clear from a consideration of the essential parts shown in conjunction with Figs. 1 to 12 how the several parts would be assembled.

Figs. 14 to 18 show circuit arrangements for a switch and its control mechanism according to the invention. Of these figures Fig. 14 shows circuits suitable for the switching mechanism used as a group selector, Figs. 15 and 16 show circuits for a discriminating selector in which the switch is required to extend a connection in two directions at the same time and Figs. 17 and 18 show circuits which may be employed in the case in which the incoming call is received over one set of multiple conductors and is extended by the switch over another set of multiple conductors. Such a use may be found in the case of a switch in a P. A. X. which acts as a line finder and as a connector.

Reference now bemade to the embodiment shown in Figs. l' to 12'.

The frame for 10. switches and a common controlling. mechanism: comprises four vertical angle iron members I, one at each corner 01 a rectangle, four transverse angle iron members 2, two at the top and two at the bottom secured controlling mechanism Parallel with the rods 3 are T shaped members 4 two for each switch and two for the control mechanism, the flanges of whichare secured tc'the outside of the flanges of the horizontal members 2, the webs projecting into the switch assembly. The webs are slotted for a distance at the ends and adjacent to the flanges to allow them to pass over the flanges of the members 2. The function of these T shaped pieces is to act as guides for re individual switches.

A switch comprises a flat plate 5 cut so as to form a number of prongs joined together at one long end, each prong carrying the contact ing parts for effecting connection with any outlet in a level, theoutlets associated with the parts on each prong being the equivalent of a level in the well. known two motion switch. The edge of the plate joining all the prongs is held between two angle iron members 6 provided with L. shaped brackets l secured to the angle irons 6, the other limb of the bracket being drilled to embrace a vertical rod 8 provided at each end with an adjustable cap 9 the head of which is slotted to engage the web of the member 4'. The cap 9 is constructed as follows: A tubular member is threaded externally at one end and is provided with a flange at the other end and a tubular collar is passed over it to within a short distance of the under side of the flange. The collar is held in position by a nut on the threaded end of the tubular member which is held on the vertical rod 8 which passes through it by. a grub screw, the collar being slotted to permit. of access to this screw, and the rod 8 being recessed to allow the grub screw to grip it. Between the collar and the flange of the tubular member at each I end of a rod 8 is held a slotted end of a flat strip Iii running parallel with pieces and held at its other end ina similar manner in another vertical rod. To a strip it are secured two angle irons I, Figs. 2 and 3, spaced so that a flange of each stands up against each side of the web of the piece 4'providing a guide for and guarding against sideways movement of a switch plate when the switch isbeing inserted or with drawn. The prongs of the plate 5 which may a be stiffened by pieces of metal attached to them on each side, are wedge shaped at the free ends and adapted to engage correspondingly shaped recesses in a member [2 attached to angle irons 13 similar to the members 6 and held to a vertical rod similar to tat what may be termed the back of the switch assembly. Also secured to the vertical rod 8 is a collar M slotted along its cylindrical surface for a short length from one end to provide a recess into which a plate [5. enters. and is held. {There is a plate H for each switch and: it" lies in the same verticali plane as the corresponding switch plate- 5 and is held-L in. a. suitable: manner! to the lower member ml. The plate I5 is shaped as shown in Figs. 3' and 4- and provides a. base plate forthe: switch operating mechanism, the plate being cut away as required.

ecured to a bracket on' the base plate and lying within a cut out. portion. thereof with its axis inthe'plane of= the: platev is the switch operating magnet M. The armature of the: magnet is provided with anextension: carrying a pawl t6. working between two stops an'd adapted? to en:-

a ratchet wheel: [:15 mounted on ahollow pin. passing through the plate I5 Also. carried by the pin is a further ratchet wheel [8, on the opposite side of the plate [.5 and adapted. to be engaged by a. springv controlled detent I 9; pivoted at 20. On the: outsideof the ratchet wheelld and'mounted on: thepin. isa disc with a. peripheral projectionv 21- at one point which is. bent at right-angles tothe plane of the disc, so as to protrude through asegmental slot in. a plate 22 mounted outside it, the plate, disc and ratchet wheelsall being held together between washers clamped. by a bolt passing: through the hollow pin.

The ratchet wheels when rotated tension a spring 23 anchored to. plate I5 and. to an arm on the ratchet wheeli H to provide for their return when the pawl l6 and'd'etent t9 are disengaged. A heel piece attached to the magnet armature is adapted tooperate contact springs m.

Carried by the plate 15 is a pair. of trip rods 2 1 and 25, rod 25 lying between. rod. 24 and the plate i5, the rods being held by screws passing through slots in them-.. The rod. 24 is of the shape shown in Fig.. 3 and rod 25 is similar. A switch plate is provided with. knife edges t2, which inthe normal. position rest on. the upper edgeof. the trip rod 24 near ramps at its ends, the upper edge. of rod 25: being somewhat below that of rod 24. When. the switch is in its normal position: as illustrated a trip latch 26 secured to the left hand end of rod 2:: (Fig. 3) engages the projection 21 associated with the ratchet wheel assembly referred to, the low edge of the projectionbeing also in engagement with the trip latch on rod 25 the two rods being held against. the projection by the springs 21 and 28. On the same side of plate [5 as the trip rods is mounted. a restoring rod 29 having a latch 39 and normally held against the tension of spring. 31 by means of detent 32 pivoted at engaging a notch in the rod; The rod can pivot about the securing screw 33 so that when it is moved to the right (Fig. 3) its left hand upper edge which is cut away engages projections on the trip' rods. In its movement to the left during its operation after release it is guided by a cam 34 fixed in a suitable position but adjustable as to its bearing on th ramp on the lefthan'd: edge of the rod 29,. the ramp being kept in contact with the surface of the cam 34 by'means of spring 35.- The adjustment of the cam will be referred to later.- The rod 29 after release by the detent 32 is restored by an arm: 36 mounted on a rotatable shaft 31 running beneath and at the back of the switch assembly. On the under side of the upper part of trip rod is a projecting piece as bent at right angles and adapted, when the rod is released to engage the upper part of detents i9 and 32 to disengage them from the wheel i8 and the restoring rod: 29 respectively;

The trip latches are suitably bent near their free ends to allow the projection 2| to move behind them after the trip rods have been released.

Pivoted to a pin passing through the plate |5 near its left hand end (Fig. 3) and at the back thereof is an oscillating member 38. This will be seen from an inspection of Fig. 4 which should now be referred to. To a projecting part on the member 38 is secured a pin 39 adapted to enter recesses in the trip rods 24 and 25. In the normal position of the switch the pin rests on the upper edge of rod 24 and when this rod is released the recess in that rod is brought into line with the recess in rod 25 and the pin falls into the recess the member 38 turning about its pivot so that its under side presses on the contact springs FD closing them. When the rod 25 is released the pin 39 is lifted from the re cess on to the upper surface of the rod and the contact springs FD are opened. At the same time a pin on rod 25 has moved away from one limb of a crank 40 which is turned in a counterclockwise direction by means of the spring 4| when the member 38 is restored, the other limb of the crank 40 engaging thecontact springs SD to operate them. During the restoration of the trip rods both of them move together so that the pin 39 does not drop into a recess and the contact springs FD are not operated. The springs SD are restored by the turning of member 40 due to engagement of the pin on the rod 25 with the upper member of the crank.

Running from the front to the back of the switch are a number of rods 42 there being two for each level. These rods are held in the vertical members by means of nuts and a rod is furnished with a number of spacing pieces 43 over the major portion of its length which is of larger diameter than its ends and between which are clamped by nuts at the end of the large diameter part transverse carrying strips 44. Held to each side of a strip 44 are guide rods 45, 46, by means of screws passing through slots in the guide rods. The guide rods extend over all the switches in the assembly and a rod 42 carries as many guide rods as there are outlets from a level. In the example illustrated the switches have ten levels of contacts in the multiple, each level having ten outlets which are multiplied over the switches of the assembly. A guide rod is formed of a flat strip cut so as to leave projections from its upper edge there being a projection corresponding to each switch in the assembly.

These projections are bent over at right angles to the plane of the strip 45, 4Giand away from the carrying strip 44 and are adapted to engage contacting springs mounted on the switch plates. The guide rods are maintained in and restored after operation to a normal position by means of springs, e. g. the spring 50. Their ends which project beyond the switch assembly into the control mechanism are turned at right angles as will be seen in Fig. 5. Also carried by the strip 44 and spaced from it on either side are strips which form the multiple. On each side of the strip 44 there are three such multiple strips 41, 48, 49 providing the test conductors and the two speaking conductors. Each strip has upstanding projections spaced along its length to correspond with the spacing of the switches, the three strips of a set being displaced longitudinally so that the projections are not in line. The several projections along the length of a set of strips form a multipled outlet of a choice the end of a test conductor 47 of a set being seen projecting into the controlling mechanism in Fig. 1 and the projections on the speaking conductors being shown in either side of those of the conductor 41' in the sectional view in the cut away portion of Fig. 1.

Reference will now be made to the contacting springs mounted on the switch plate with reference to Fig. 3 and the perspective views in Figs. 6 to 10. On each of the prongs of a switch plate 5 are secured and insulated from it conducting members 5|, a member having integral with it a number of flexible contacting members herein referred to as contacting springs. The members 5| are held against the prongs of plate 5 by a face strip 86. Each contacting spring 52 is in the form of an elongated U with its limbs parallel with the conducting strip to provide the requisite flexibility the end of one limb of the U extending at right angles and being connected with the conducting strip 5| the end of the other limb being shaped to provide a dependent portion 53 which is turned back in the direction of the limb and parallel to it. This portion, in the case of one of the contacting members extends also in the other direction for a length sufficient to extend over the multiple conductor nearest to the carrying strip 44. The other two contacting members are formed in a similar fashion but with a tooth depending in line with the corresponding multiple projection, the spring being cut away between the tooth and the backwardly projecting part to avoid contact between one spring of a set and a multiple conductor corresponding to another of the set when the springs are brought behind a multipled outlet with which contact is not to be made. The three contacting springs and the members 5| are separated from one another by insulating strips. The backwardly extending parts 53 of the three springs of a set lie close to one another but separated by insulation and are adapted to be moved laterally by a projection 55 on a guide rod.

In order to effect a connection a switch plate is lowered in a first stage by releasing trip rod 24 after which a guide rod corresponding to a selected outlet choice in the required level is operated and the switch plate is then lowered in a second stage after which the guide rod is restored. These operations will be described in further detail later. Referring now to the perspective views, Fig. 6 shows a guide rod and a set of contacting springs of a switch plate in the normal position. It will be seen that if the guide rod 45 is moved to the left the projection' 55 will pass beneath the turned back part 53 and the contacting springs will be unaffected. In Fig. 7 the switch plate has been lowered in its first stage and the projection 55 on the guide rod will be seen to be in line with the part 53. When the guide rod is moved to the left the projection 55 pushes against the part 53 and the springs are flexed so that instead of being in a plane behind, that is, to the right of the multiple strip projections 41, 48 and 49 they are in a plane in front of them. When the switch is lowered in its second stage the teeth of the contacting springs will lie in front of the multiple projections and when the guide rod is released will be pressed firmly against them due to fiexure of the springy members. These positions are shown in Figs. 8 and 9. Fig. 10 shows the position of the contacting aoossrsz teeth behind the multiple projections of a switch which has been lowered in its second stage but the outlet shown .is not the one selected that is to say the guide rod shown in this figure has not been operated. The electrical connections to the contacting springs 51 may be made by conn cting together .all the contact springs of the several levels and connecting them by flexible connections to knife edge contacts mounted at a convenient position andengaging jacking points mounted on the frame. The electrical connections to the magnets M and its contacts and contacts ED and SD may be made in a similar manner.

Reference will now be made to the common controlling mechanism and Figs. .1, 2, 5, ll and 12. A pair of vertical rods 54 similar to the rods 8 and supported in .a similar mannerhave angle iron members 55 secured to them by means of brackets similar to the brackets l. Secured to the angle irons 55 and near theirlowe-r :ends isa plate bent into a rectangular form of three sides only. Across the end of the assembly and also secured to the angle irons is a plate 58, provided with knife edges .59 which rest on a slidable rod 60 resting in brackets 6! carried by the rods 54. Therod-BU has two elevated portions on which the knife edges rest and when the rod is slid outwards (to the left in Fig. 2) the knife edges slide down the ramps on the plate 60 and rest on the lower part of the upper surfaces and the whole mechanism is lowered to enable it to be withdrawn.

Mounted on the back of plate 57., that is on the side next to the switch assembly are the guide rod magnets GM. The magnets are :arranged in pairs the armatures of apair being secured to a guide rod shaft 62 journalled in a plate secured to the magnet yokes. The armatures are biased by a spring for'example, so that they normally assume the positions shown. Also mounted on the back of plate 51 are the cam shaft magnet CM and the shift rod magnet SM. The formeris provided with an armature and pawl adapted to engage a ratchet wheel 63 on the cam shaft 64 journalled in a plate 55 formed by bending over the top of the plate 57. The shaft 64 is provided with a number of earns 80 the noses of which are helically displaced around't-he shaft and are situated opposite each level on positions on the shaft corresponding to each level. The cam shaft is held in a normal position by means of a spring (not shown). The magnet SM oscillates a shaft 65 by means of its armature which is provided with an extension acting on a detent 66, which, when the magnet SM is energized is disengaged from the ratchet wheel 63 to allow it to; return to its normal position when the pawl controlled by magnet GM is disengaged on the release of that magnet. Mounted on the front plate '58 is the restoring magnet RM which, by means of an armature extension oscillates the restoring rod 31.

At the upper ends of the angle irons 56 is secured another plate 61 bent and secured in a similar manner to the plate 5'! but provided with a bottom which may be bent up from the back. The bottom provides journals for the guide rod shafts, cam shaft and shift rod shaft, 54 and 65. To the back of this plate are secured the test relays T. A plate '68, similar to the plate 53 is provided near the upper end of the angle irons 5S.

Secured to the ends of plates 51 and 61 at the front and back of the assembly are momhers-.10 provided with slots at each level of the switch in which the shift rods (83 .lie. -Each shift :rod :is provided with .a number of projections 69 adapted to bring contact fingers-ll into engagement with the test conductors 47 of the outlets of the corresponding level and to bring the guide rods 45 and 46 into operative conjunction with the arms 12 secured tothe shafts .62 at each switch level. These may be seen in Fig. 2 forthe shift rod of the 1th level counting upwards where the guide rod. and other shafts have been broken away for the purpose. The contact fingers M are flexible and are secured to stiff vertical members 713 which run vertically from; the top to the bottom. of this assembly. Eachmember 13 carries fingers for the same outlet choice of all the switch levels and is clamped to transverse rods 14 held to the angle irons '56 by! plates 15 and electrically connected to a test relay T.

Near its back end ayshift rod is under the control of a lever 16,, the several levers, one for each switch levelbeing .loosely mounted on a vertical shaft 1:1. At-the end remotefrom theshift rod connection the lever is notched and the end of a flexible pawl 19 attached to arm 18 mounted on the shift rod shaft 65 is adapted to be brought into operative conjunction with the lever by means of the relevant cam 80 on the shaft 64 when the magnet .SM is energized and the pawl engages the notch and operates,

the lever which is held so long as the magnet SM remains energized. i

The restoring magnet RM actuates the restoring shaft 31 which runs behind and below the switches of an .assembly by means of a lever 8|, an arm of which operates contactsqrs in a manner to be described; armature .O magnet RM also :act-uates contacts rm.=.The' restor ing shaft is provided with 13.11 arm '36' forfeach switch and when the rod is oscillated theseveral. arms are brought into contact with I the restoring rods 29 .of released switches to bring about their restoration.

If it is desired to withdraw a switch from the assembly the nuts on the-caps 9 of the back rod of the switch are slackened and by gripping the rod it may be withdrawn taking with it the angle iron members 13 and the guide member 12, the-rod pulling out of the slotted ends of the member 1:0.

By gripping the front rod 8 of the switch the switch plate 5 andbase plate 1 5 may be withdrawn from the front of the switch the plate being prevented from tilting by means of the angle iron members I] at the top and bottom. It will be .seen from Fig. 3 that they-withdrawal of a switchmay be carried out without disturbing the multiple :or the guide rods,'the electrical connec-tionsbeing made over knife" edge contacts or by easily undone connections as already ,explained.

To withdraw the common controlling mechanism the rod 60 is pulled towards the front of the assembly permitting the whole mechanism to be lowered from the elevated part of. the upper edge of the rod 60 to the lower part of this edge. This lowers the fingers H clear of the test conductors :and the shift and guide rod operating members clear of the multiple and guide rods. By gripping the front rod the whole mechanism may be withdrawn from the front, the electrical connections to the magnets and relay being made as before.

When either a switch or the common control 

